Treatment of chrome leather and preparation of vegetable retanning material used in the process



United States Patent Oflfice 3,080,206. Patented Mar. 5, 1963 TREATMENTOF CHROME LEATHER AND PREP- ARATEGPJ 6F VEGETABLE RETANNHNG MATE- REALUSED IN THE PRQQESS Carl G. Telander, Ashtabula, @hio, and Melvin L.Herman, Sheboygan, Wis assignors, by mesne assignments, to Armour aCompany of Delaware, (Ihicago, 11]., a corporation of Deiaware No Draw"ting. Continuation of application Ser. No. 442,896, Early 12, 1954.This application Feb. 11, 1959, Ser. No. 792,461

12 Claims. (Cl. 84-.26)

This invention relates generally to the tanning of leather. Moreparticularly, this invention relates to an improved process of retanningchrome tanned leather in the manufacture of retan leathers. Thisinvention also relates to the processing of runaway liquor in preparingnovel vegetable retanning compositions for the treatment of chromeleather.

Vegetable tannage or mineral tannage have long constituted the majortanning processes in the manufacture of leathers of different types.Each process has its advantages as Well as limitations and the choice ofmethod is necessarily determined on the basis of the properties of theleather desired and other considerations such as cost, availability ofreagents, etc.

The vegetable tanning process, for example, is desirable particularly inthe tanning of heavy leathers such as sole leather since superiorPlumping and fullness is obtained thereby accounting for high yields ofleather from the hide or skin stock. The rate of diffusion of vegetabletannin into hides, however, is very slow and a long time is required tosufficiently tan the hide. The use of concentrated vegetable tanningliquors to circumvent the slow diffusion has not proven successful sincethe rate of combination of the tannin with the protein of the hide isgreater than the rate of diffusion of the tannin into the interior ofthe hide. Consequently, the outer layers of the hide become contractedto a greater extent than the inner layer and a distortion results whichdetracts from the appearance and value of the leather. To overcome thisdifiiculty, tanners are compelled to use a multiple step process whentanning with vegetable tannins which involves the moving of the hides orskins into progressively stronger tanning liquors until they arecompletely tanned. In some cases, as in the tanning of sole leather,months may be required to complete the tanning of the leather.

Mineral tannage, on the other hand, the most Widely used process beingchrome tanning, is capable of drastically reducing the period requiredfor tanning the hide or skin stock. Chrome tanning also imparts to theleather the properties of greater resistance to heat and abrasion thandoes vegetable tanning. Although a good portion of the worlds supply oflight leathers is tanned by means of chromium salts, the chrome tanningprocesses are incapable of producing the properties of plumpness,fullness, and other characteristics required for many specific uses forleather.

Several approaches have been used in attempting to overcome the abovedifiiculties and limitations. One approach has been the search for newtypes of tanning materials commonly referred to as syntans. Another hasbeen the use of combined chrome and vegetable tannage using, forexample, a chrome tanning operation first and then vegetable tannage orvice versa to supplement or combine the characteristics or resultsinherent in each tanning process. The products from such combinationtype of tanning process are called retan leathers.

In effect, the chrome tanning step when used in combination with avegetable tanning step makes it possible to more or less average theadvantages and disadvantages of both tanning procedures. The chrometanning or pretanning thus enables a rapid penetration of the mineraltanning liquor into the entire mass and imparts to the leather theimproved resistance to heat and abrasion. The chrome leather is thensubjected to the action of fresh vegetable tanning liquors to permit thedesired degree of retanning to occur whereby a plumper and fullerretanned product is obtained. Other changes such as properties pertinentto tooling "and embossing the leather are also significantly improved bythe retanning.

One basic disadvantage of the combination tannage is the increased costof tanning reagents inasmuch as both the chrome tanning and vegetabletanning reagents are necessarily involved in the process. The cost ofthe relatively expensive vegetable tannin materials is a particularlyimportant factor in the production of retan leathers.

We have now found that chrome leather can be retanned by treating thesame with concentrated runaway liquor. Surprisingly enough, this spentvegetable tanning liquor which heretofore has been considered to be ofno value for further vegetable tanning purposes has now been found to bean excellent retanning agent for chrome leather. Until the presentdiscovery, the discarding of this runaway liquor has constituted a majorwaste disposal problem. In addition to eliminating this waste disposalproblem, the newly discovered utility of this formerly rejected materialnow makes possible the retanning of chrome leather at a substantiallylower cost. The retan leather made in accordance with the presentinvention is not only as good as the chrome leather conventionallyretanned with fresh vegetable tanning liquor but is actually superior inso far as qualities and properties such as grain texture and strength,yield of leather breaking characteristics, feel, etc., are concerned.The runaway liquor concentrate described hereinafter in detail has alsobeen found to be highly desirable as a color mordant for chrome-tannedleather.

It is therefore an object of this invention to provide a process forretanning chrome leather without requiring the use of fresh vegetabletannin liquors heretofore used in the process for vegetable retanning ofchrome leather. It is another object to provide a process for retanningchrome leather wherein runaway liquor extract can be utilized as acomplete or partial replacement for natural vegetable tanning substancesas the retanning agent. It is another object to provide novel retanningmixtures useful in the treatment of chrome leather. It is a furtherobject to provide a process for retanning chrome leather at asubstantially reduced cost. It is yet another object of this inventionto provide a process for applying spent vegetable tanning liquors aftertreatment of the same to retanning and mordanting of chrome leathersthereby eliminating a Waste disposal problem. Yet another object is toprovide a chrome leather retanning process which results in theproduction of retan leathers having superior tooling and embossingcharacteristics as well as improved grain texture and strength, yield,feel, appearance, etc. Yet another object is to provide a process fortreating runaway liquor for converting the same to a desirable form forutilization as a vegetable retanning and mordanting agent for chromeleathers. Further objects ment.

and advantages will appear as the specification proceeds. Conventionalvegetable tannery liquor is made up of extracts from quebracho,chestnut, wattle, valonia, myrobalons, spruce, gambier, divi-divi, andother nut, wood, root or bark concentrates. Following its conventionaluse in vegetable tannery operations wherein the active tannin content isconsidered substantially exhausted to a degree wherein the liquor is ofno further use for tanning purposes, this material depending upon itsinitial composition and the vegetable tanning process in which it hasbeen used has the following approximate composition:

Total solids percent 2.8-3.6 Soluble solids do 2.63.1 Insolubles do0.2-0.5 Non-tannin do 2.02.3 Tannin do 0.6-0.9 Purity 23-28 pH 5.0-5.5

The spent vegetable tanning liquor constitutes the socalled runawayliquor the bulk of which is routinely discharged to sewers therebycreating a serious disposal problem. Usually, active remedial stepsinvolving substantial cost must be taken to eliminate odor and pollutionproblems created by the waste disposal. Some limited uses of thematerial have been heretofore made as, for example, in connection withthe treatment of boiler water, oil well applications, leather dressing,etc., but such uses have resulted in the utilization of only smallquantities of the available runaway liquor resulting from vegetabletanning operations.

This invention is based in part on the discovery that runaway liquorconcentrates prepared in accordance with the process hereinafterdescribed in detail can be used as a retanning and mordanting agent forchrome leather. Although this material is by no means a suitablesubstitu te for fresh vegetable tanning liquors in so far as vegetabletanned leather is concerned, it has now been found to be an excellentvegetable retanning agent for chrome leather in place of the freshvegetable tanning liquor heretofore required for the purpose. In otherwords, despite the fact that the components in the concentrate aresubstantially rejected in conventional vegetable tanning operations, inthe case of chrome leather, an almost complete takeup of the tannin,insolubles and non-tannin occurs. Thus, the processed runaway liquorwhen used for retanning chrome leather functions in a manneli similar tofresh vegetable tanning liquors'resulting in an almost completeexhaustion of the liquor- In .the case of the runaway extract, thenon-tannins appear to be taken up by the leather to an even greaterdegree than the non-tannins of natural vegetable tanning extracts. Themechanism for this phenomenon is not clear-;

1y understood but the'specificity of the action as being related to theprior chrome tanning treatment of the leather is clearly established.

' This discovery is of great importance since in addition to virtuallyeliminating a serious waste disposal problem, a much more inexpensiveretanning and mordanting liquor is made readily available for thetreatment of chrome leather. Atthe same time, chrome leather treatedwith the runaway liquor extract is of better quality than when retannedwith natural vegetable tanning agents in accordance withconventionalpractice. This improve ment of quality of the finishedleather is particularly evident in the flanks and heads as compared toleather retanned with conventional fresh vegetable extracts. The,treatment of runaway liquor or vegetable tanning sewer liquor prior toits utilization as a retanning or rnorda nting agent for chrome leathercan be readily achieved on a commercial basis in conventional equip-Prior to the processing of the waste liquor, the discharge liquor fromthevegetable tanning rocker sec tions is collected in a tank and allowedto settle for a brief period. Prolonged standing and the use of dirtytanks should be avoided to prevent excessive contamination and bacterialdecomposition which cause undesirable odor development. Solid materialsof relatively large particle size such as fibrous flesh materials, barkfragments, etc., are easily removed by screening the liquor. The nextstep of the treatment comprises concentrating the total solids contentof the runaway liquor from the previously indicated 2 to 4% level to anydesired value dependent upon the requirements of the subsequentretanning or mordanting procedure in which the concentrate is to beused. For most chrome leather retanning processes, it is desirable tohave retanning liquors containing total solids ranging from 20 to 45% byweight or more depending upon the fluidity, ratio of tannins tonon-tannins present, insolubles, etc. In order to reduce handling andshipping costs, it may be desirable to evaporate the runaway liquorextract to complete dryness or powder form by conventional spray orflash drying methods. The concentrate in either the liquid or powderform can be readily reconstituted or adjusted to any desired totalsolids level prior to its mordanting and retanning usage without anyloss or. impairment of the retanning or mordanting properties of thematerial.

For evaporating or condensing runaway liquor, conventional equipmentsuch as single stage, double stage or multiple stage evaporators can beused. Triple effect vacuum evaporators have been found to be especiallypractical for processing runaway liquor in commercial quantities.

The condensation or evaporation treatment produces certain changes inthe non-tannin content of the liquor. Although the mechanism for thechanges is not fully understood, it can be readily determined bystandard tannin analyses and evaluation of the purity that a conversionof non-tannins to tannin actually occurs. If no changes in non-tanninsand insolubles took place, the composition of the tannin in theconcentrate would vary only in proportion to the extent ofconcentration. Such is not the case, however, as seen from the followingdata which are representative of the values at various stages of thetreatment of runaway liquor as compared to calculated values which wouldotherwise be expected if no conversion of non-tannin to tannin occurred:

Although the conversion of insolubles and non-tannins materials variessomewhat depending upon the starting material as determined by thecomposition and usage of the original vegetable tanning solution, theincrease in active tannin is nevertheless consistently obtained byvirtue of the evaporation process. The more pronounced conversion ofnon-tannins to tannin is indicated by the relatively higher total solidslevels as compared to concentration of total solids to below 20% orthereabouts.

In view of the enhanced conversion of insolubles and non-tanninsubstances in the liquor to tannin previously described, however, it isaccordingly preferred to concentrate the total solids at least to 20%and preferably to about 35 to 45%. The tannin content of concentrates ofabout 42% total solids on the basis of overall composition ranges fromabout 8 to 15% by weight of the total solids therein and the concentratein this form provides an excellent vegetable retanning liquor for chromeleather.

As previously indicated, the non-tannins and insolubles present in theconcentrate are also consumed in the retanning process. Therefore thehigh degree of retanning action achieved by the use of runaway extractcannot be explained solely on the basis of the tannin content alone.Although the mechanism of the retanning action is not clearlyunderstood, it is believed that the non-tannin content acts as a bufferthereby preventing drawing of the grain of the leather particularly inthe neck and flank portion of the hides.

The use of the concentrates prepared from difierent sources inaccordance with the method herein disclosed occasionally results inconsiderable variation of the color of the finished leather when appliedto the retanning of chrome leather. For eliminating or minimizing thisdifficulty, changing the dyes used in coloring the leather has beenfound to be helpful. Color improvement may be more effectively achievedhowever, by lowering the pH of the concentrate. Further improvement ofcoloring properties and characteristics is obtained by adding asequestering agent which modifies the effect of iron and other metalsalts present in the concentrate through its chelating action. The useof both measures are preferred for establishing a firmer combination ofthe retanning ingredients in the leather and improving the coloringproperties of the concentrate.

The acids which may be used for lowering the pH may be either organic ormineral acids including acetic, oxalic, lactic, formic, citric,hydrochloric, sulfuric, phosphoric acids, etc., or mixtures thereof.Very good results are obtained, for example, by the use of combinationsof acids such as acetic-hydrochloric or sulfuric-oxalic, etc.

The amount of acid to be used can be varied rather broadly but the pHadjustment should not be excessively low (below 4.0) since thepenetration of the concentrate is adversely affected. The use of runawayconcentrate at a pH below about 4.0 also causes a pile-up on the grainresulting in a dry crust break of the leather. The adjustment of pHbetween the range 4.1 and 5.8 is generally satisfactory but it ispreferred to adjust the pH to between 4.5 and 5.5 with about 4.7 beingthe optimal pH value. The acid or acids used for adjusting the pH of theextract may be incorporated into the concentrate either during thecondensation process or prior to the utilization of the concentrate inthe retanning or mordauting process.

sequestering agents of various types can be used for improving thecoloring properties of the concentrate. Commercially availablesequestering agents of the ethylenediamine tetraacetic acid type and itssalts are especially desirable. Excellent results are obtained by theuse of the various sodium salts thereof. The quantity of sequesteringagent to be added to the concentrate can be varied broadly as from .05to 2% by weight based on the weight of the concentrate in either liquidor powder form. Good results are obtained when from .1 to .2% by weightof the sequestering agent is added to the evaporated extract containingabout 4045% total solids.

In a preferred process for preparing the concentrate of extract fromvegetable tanning runaway liquor, the accumulated liquor is screened andevaporated in a tripleefiect evaporator to concentration ofapproximately 20 to 30% by weight of total solids. This concentratereferred to as first run extract is allowed to settle in a tank wherebythe coarser insoluble particles become separated and are removed. Thefirst run extract is then further evaporated to about 42% total solids(second run extract) after which the pH is adjusted to approximately 5.0by the addition of hydrochloric acid. Sufficient acetic acid is thenadded along with about .15 of sequestering agent (based on the weight ofthe second run extract) to adjust the pH of the concentrate to about4.7.

During the evaporation process, conventional antifoaming agents can beused if desired to eliminate or minimize losses of the material causedby excessive foaming. A further modification consists of the addition ofa masking agent to improve the odor characteristics of the product.Preferably, the masking agent should also possess bactericidalproperties for improving the keeping qualities of the concentrate.Silicofiuoride salts, phenolic compounds, mercurials and otherpreservatives can be used but it is preferred to use phenolic compoundssuch as phenol, cresol, etc. Mixed cresols or cresylic acid areparticularly desirable when added in concentrations up to about 0.5% byweight with the preferred concentration of masking agent being withinthe range of from 0.03 to 0.1% by weight.

It is to be understood that the preferred embodiment for preparing theconcentrate containing about 42% total solids disclosed above merelyrelate-s to a desirable composition and to a convenient procedure forpurposes of handling, shipping, fluidity, etc. Accordingly, it is notintended to be limited thereby as to the specific degree ofconcentrations of the runaway liquor and to the manner in which theconcentration is achieved. The two-step evaporation, for example, is notessential since the evaporation to any desired level of total solids canbe achieved directly or in a single step and, as previously indicated,the evaporation can be continued until a solid material is produced asby spray or drum drying without adversely aifecting the efiicacy of theconcentrate in the retanning and/or mordanting processes for chromeleather.

For treating chrome leather with runaway liquor concentrate or extract,any of the conventional vegetable retanning procedures for chromeleather can be used. The concentrate may be used as is, depending uponits total solids content as determined by the degree of concentration orit may be diluted or reconstituted for use in the retanning process. Theextract can also be used alone or with other materials as a vegetableretanning and mordanting material on chrome leather. The pH of theleather can be adjusted during the course of the retanning procedure asdesired without impairing the retanning properties of the extract orcausing undesirable pile-up of the grain. Organic acids such as acetic,formic, lactic, oxalic, etc. are conventionally used for this purpose.

The quantity of runaway concentrate to be used in treating chromeleather can be varied considerably depending upon the degree ofretanning desired in the leather and also upon the total solids contentof the specific run away liquor extract being used in the process. As amordant for the dyeing of chrome leather, for example, only a lightsurface treatment is usually involved and the quantity of total solidsabsorbed by the leather during such treatment is about 2 to 6% by weightbased on the weight of the shaved chrome stock. Thus the total amount ofthe concentrate can be readily calculated on the basis of its knowntotal solids content in any given case thereby making available to thechrome leather the predetermined amount of total solids.

The quantity of run-away concentrate to be used for retanning chromeleather is similarly calculated on the basis of the weight of the shavedstock. Depending upon the degree of retanning desired and also upon thesource and quality of the leather stock being treated, extensivevariation as to the quantity of retanning agent are necessarilyinvolved. In terms of absorbed total solids by chrome leather, theuptake of the tannins, non-tannins and insolubles can vary from aslittle as 6 to 15% of its weight to as high as about 25% in the case ofheavy retannage of sole leather. Whereas the tannin content of thenatural vegetable liquors heretofore used for retanning chrome leatheris determinative of the amount to be used in a given retanning process,the method of determining the amount of concentrates should take intoconsideration the non-tannins and insolubles in view of the importanceof these components in the retanning process. By way of illustration, ifa heavy degree of retanning is desired,

proximately 42% by weight of total solids.

.about 60% by weight of-runaway liquor extract containthe retanningmixture about 25% total solids on the basis of the weight of the shavedchrome leather. Lesser quantities or diluted solutions can be useddepending upon the required specifications of the finished leather andthe type of chrome leather being treated. Thus it is seen that thetechniques and procedures for retanning chrome leather in accordancewith conventional practices involving vegetable retanning of chromestock are generally applicable to the retanning process hereindisclosed, the essential difference being the utilization of the runawayextract as a complete or at least a partial replacement for new naturalvegetable retanning materials.

The retanning procedure can be further modified to include the use ofboth the runaway concentrate and fresh vegetable tannin liquor by eitherutilizing a mixture of the two retanning agents or by subjecting thechrome leather to the action of each in separate processing steps. Forpreparing the mixture for simultaneous use in a onestep process, thequantity of each retanning agent can be varied from a small proportionof runaway liquor extract up to a point where practically none of thenatural vegetable tannins are present. By way of illustration, a highlysatisfactorily finished leather can :be obtained by treating chromeleather in one operation with a retanning blend consisting of 75% byweight of the concentrate (42% T.S.), the balance of the material beingfresh vegetable tanning liquor prepared from wattle or quebracho, etc.The total quantity of the blend to be used depends merely upon thedegree of retannage desired for the finished leather.

The two-step procedure can likewise be varied broadly as to the ratio ofthe concentrate to fresh vegetable tanning liquor to be used. In thisprocedure, it is preferred to subject the chrome leather to theretanning action of the concentrate and after a light washing, theleather is further treated with fresh vegetable tanning liquor. Oneembodiment of this process involves treating chrome leather successivelywith equal weights of the concentrate (about 42% T5.) and freshvegetable tanning liquor respectively.

The general method of application of the runaway liquor concentrate as aretanning agent for chrome leather is to add it in a suitable dilutionto the drained and shaved chrome stock in a revolving drum. The quantitywill vary with the type of leather produced but may reach up to about 50to 60% of the leather weight on the basis of runaway liquor concentratecontaining ap- As previously stated, the retanning may be carried outexclusively with the concentrate or it may be effected by supplementingthe same with varying amounts of fresh'vegetablev tanning liquor eitherin admixture therewith or used separately as a two-step retanningoperation. In either event, there is no specific limitation upon thequantity of runaway liquor concentrate or upon the ratio of the same tofresh vegetable tanning materials which can be used other than theindividual requirements of any given retanning process as determined bythe degree of retanning desired in the treatment of chrome leather.

For a fuller understanding of the nature and objects of the invention,reference should be made to the following examples which are given toillustrate the invention:

EXAMPLE I In a series of runs involving the daily supply of runawayliquor made available from conventional vegetable tanning operations,the liquor was evaporated in a tripleeifect evaporator to concentratethe total solids content to approximately to 30% total solids and atthis stage was held in a tank to permit settling and removal of thecoarser insoluble particles. The material was then further evaporated toyield the finished extract (untreated) the compositions of which areindicated in Table I.

'lbs. of concentrate (untreated).

Table I Run Total Soluble solu- Non- Tannin Purity pH Ash solids solidsbles tannin Percent tannin X 100 Percent soluble solids Percent tannin X100 Percent non-tannins percent tannin EXAMPLE II Runaway liquorconcentrate prepared in accordance with the procedure set forth inExample I was further processed following the second evaporation step bythe addition of hydrochloric acid with stirring to bring the pH between5.1 to 5.0. Sufficient acetic acid was then added to further lower thepH to 4.7 after which 0.15% by weight of the sequestering agent(sodiumsalt of ethylenediamine tetraacetic acid) was added. Finally,while still stirring the mixture .05% by weight of cresylic acid wasadded to produce the treated concentrate.

When used in mordanting or retanning chrome leather, the treatedconcentrates as opposed to the untreated concentrates showedconsiderably improved coloring properties. The odor of the materialitself as well as that of the finished leather was also substantiallyimproved. A further advantage consisted of vastly improved keepingqualities of the material when kept under typical conditions of storage.

EXAMPLE III A tank car of runaway liquor amounting to 67,300 lbs. ofliquid after separation of sediment was processed in a triple-effectevaporator to yield approximately 5000 A small portion of theconcentrate was kept for analysis and evaluation and the balance waspumped into a mixing unit. A sequestering agent was added to aconcentration of .4% by weight a (205* of sodium salt of ethylenediaminetetraacetic acid) based on the Weight of the concentrate and the mixturewas stirred 15 minutes. The pH was then lowered by the gradual additionwith stirring of hydrochloric acid,

about 60 lbs. being required to bring the pH to 5.05.

Acetic acid (80%) was then added to further lower the pH and followingthe use of 75 lbs. the pH reached 4.55. The mixer was run for anadditional 15 to 30 minutes to insure thorough mixing.

The data in Table II summarizes the analytical data for the runawayliquor, the concentrate (untreated) prepared therefrom and the acid andsequestering agent treated concentrate.

Tablet]! Mois- Total 801- In- Non- Tan- Purture solids uble soltanninsity pH solids ubles nin Runaway liquor 96.27. 3.73 3.44 0.29 2.16 1.2837.2 5.2 Concentrate (untreated)- 56.73 43.27 40. 79 2.48 24.17 16.6240.7 5.6 Concentrate (treated) 57.26 42.74 40.74 2.00 23.38 17.36 42.64.6

EXAMPLE 1V 5(quebracho) and (b) the runaway liquor concentrate added tothe revolving drum and run for 30 minutes.

Analysis of both retanning agents before and after use gave thefollowing results:

Spent runaway liquor concentrate trate New quebracho Moisture percent.

EXAMPLE V In a conventional retanning process for the treatment ofchrome leather wherein fresh vegetable tanning substances are used, thenatural vegetable extract can be substituted on an equal weight basiswhen it is desired to use runaway liquor concentrate (40-45% by weighttotal solids) as a 100% replacement therefor. As in usual practice, thechrome tanned stock is loaded in a revolving drum and washed orneutralized depending upon the desired pH. The skins are covered withwater (80 F.) and the desired quantity of the runaway liquor concentrateis introduced and drummed into the stock until the total solids ar spentto about 1 to 1.5%. Thereafiter the stock is further treated inaccordance with conventional practices for the production of retanleather.

EXAMPLE VI Blend 1 Blend 2 Blend 3 Parts vegetable extract 25 Partsrunaway liquor concentrate.

Instead of using the blend, the retanning agents can be used separatelyin the two-step retanning process in which event the runaway liquorcooncentrate is first drummed into the stock using the process set forthin Example V. The stock is washed for 5 minutes and again covered withwater (80 F The natural vegetable extract is added to complete theretanning and the leather is fat-liquored and further treated inaccordance with conventional practice.

This application is a continuation of patent application Serial No.442,896, filed July 12, 1954, by the same coinventors, and nowabandoned.

While in the foregoing specification the novel retanning and mordantingmaterials and methods of preparing and applying the same have beendescribed in considerable detail by reference to specific embodimentsthereof, it will be apparent to those skilled in the art that theinvention is susceptible to other embodiments and that many of thedetails set forth can be varied widely without departing from the basicconcepts of the invention.

We claim:

1. In a process for treating animal hides wherein chrome tanned leatheris contacted with fresh natural vegetable tanning materials to retansaid leather, the improvement characterized by the step of substitutingfor at least a portion of said fresh vegetable tanning materials a spentvegetable tanning liquor concentrated by evaporation at reduced pressureto at least 20% by weight of total solids.

2. The process of claim 1 wherein the spent vegetable tanning liquorconcentrate is substituted as a complete replacement for the naturalvegetable tanning materials and the chrome tanned leather is contactedtherewith until said leather has absorbed from 6 .to 25% of its weightof total solids from the concentrate.

3. In a process for retanning chrome tanned leather the improvementwhich comprises the steps of partially retanning said leather with spentvegetable tanning liquor concentrated by evaporation at reduced pressureto at least 20% by weight of total solids and thereafter completing theretanning with fresh natural vegetable tanning materials.

4. In a process for retanning chrome tanned leather, the step oftreating said leather with spent vegetable tan ning liquor concentratedby evaporation at reduced pressure to contain from 20 to 45% by weightof total solids.

5. In a process for preparing a vegetable tanning and mordanting agentfor chrome tanned leather from spent vegetable tanning liquor, the stepscomprising concentrating said liquor by evaporation at reduced pressureto increase the total solids content thereof and adjusting the pH of theconcentrate to between 4.0 and 5 .8.

6. In a process for preparing a retanning substance for chrome tannedleather from spent vegetable tanning liquor, the steps comprisingevaporating said liquor at reduced pressure to concentrate the totalsolids therein to between 20% and 45 by Weight, adjusting the pH of theconcentrate to a pH between 4.5 and 5.5 and adding a sequestering agentthereto.

7. In a process for preparing a retanning substance for chrome tannedleather from spent vegetable tanning liquor, the steps comprisingevaporating said liquor at reduced pressure to a total solids content ofabout 20% to 45 by weight, adjusting the pH of the concentrate tobetween 4.0 and 5.8 and adding a sequestering agent and an odor maskingagent thereto.

8. In a process for treating spent vegetable tanning liquor to prepare aretanning and mordanting agent for chrome tanned leather, the stepscomprising evaporating said liquor at reduced pressure to increase thetotal solids content thereof to at least 20% by weight of total solids,adding acid to lower the pH of the concentrate, and adding to saidconcentrate a sequestering agent and an odor masking agent to improvethe coloring and odor characteristics thereof. 7 v

9. In a process for preparing a retanning substance for chrome tannedleather from spent vegetable tanning liquor, the steps comprisingevaporating said liquor at reduced pressure to about 35% to 45% totalsolids by weight, adding suflicient mineral acid thereto to adjust thepH to about 5.0, further lowering the pH to about 4.7 by the addition ofan organic acid, and adding sufiicient amounts of a sequestering agentand an odor masking agent thereto to improve the coloring and Odorcharacteristics of the product.

10. The process of claim 9 wherein the sequestering agent is .a sodiumsalt of ethylenediamine tetraacetic acid and the quantity used rangesfrom 0.05 to 2.0% by weight based on the weight of the finished product.

11. In a process for preparing a vegetable retanning substance forchrome tanned leather from spent vegetable tanning liquor, the stepscomprising evaporating said liquor at reduced pressure to produce afirst run extract containing about 20% to 30% by weight of total solids,further evaporating said extract at reduced pressure to obtain -a secondrun extract containing about 42% by weight of total solids, adjustingthe pH of said second extract to about-5 .0 with a mineral acid selectedfrom the group consisting of hydrochloric, sulfuric and phosphoricacids, further lowering the pH of the mixture to about 4.7 by theaddition of an organic acid selected from the group consisting ofacetic, oxalic and lactic acids, adding about .15 byweight of a sodiumsalt of ethylenediamine tetraacetic acid to improve the coloringcharacteristics thereof .and adding about .05% by Weight of an odormasking and .from said liquor to produce a powder suitable uponreconstitution with Water for use in treatment of chrome tanned leather.

12 References Cited in the file of this patent UNITED STATES PATENTS1,065,168 Nance June 17, 1913 1,149,298 Shaw Aug. 10, 1915 1,953,968Merritt Apr. 10, 1934 OTHER REFERENCES McLaughlin et al.: The Chem. ofLeather Manufac- 10 ture, 1945, Reinhold Publ. Co., New York, pp. 568and R.T.D.T.D.C., Vol. 45, N0. 9, September 1953, pp. 176- Progress inLeather Science, 1920-1945, London, 1948,

1. IN A PROCESS FOR TREATING ANIMAL HIDES WHEREIN CHROME TANNED LEATHERIS CONTACTED WITH FRESH NATURAL VEGETABLE TANNING MATERIALS TO RETAINSAID LEATHER, THE IMPROVEMENT CHARACTERIZED BY THE STEP OF SUBSTITUTINGFOR AT LEAST A PORTION OF SAID FRESH VEGETABLE TANNING MATERIALS A SPENTVEGETABLE TANNING LIQOUR CONCENTRATED BY EVAPORATION AT REDUCED PRESSURETO AT LEAST 20% BY WEIGHT OF TOTAL SOLIDS.